LOS ANGELES — In her four decades as America’s cooking teacher, Julia Child had a hard and fast rule about commercial endorsements: She didn’t do them. It didn’t matter whether it was the butter that made her beurre blanc sauce sing, the pot in which she slow-cooked her cassoulet or even the cookbooks penned by chef friends; her praise was not for sale.

“It was sort of a life philosophy that she had,” her great nephew, Alex Prud’homme, said, recalling how she frequently remarked, “Your name is your most valuable asset, and you should be very careful how it’s used.”

Eight years after her death, Child’s disdain for commercial endorsements is being aired anew in a legal battle pitting her heirs against the makers of what might be described as her occupational right hand — her oven. At issue in dueling lawsuits filed in recent days is a marketing campaign, launched without the permission of Child’s estate, that touts her use of Thermador appliances decades ago in her home and television kitchens.

The campaign rolled out this year by Thermador, a 96-year-old brand based in Irvine, Calif., ranged from a Facebook “like” of its products by “Julia Child, chef” to glossy magazine ads that showed photos of Child and two of the brand’s ovens with the caption, “An American Icon and Her American Icons.”

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Both sides agree that there were Thermador appliances on the Boston set where Child filmed “The French Chef” in the 1960s and 1970s and that she had a Thermador oven in the kitchen of her Cambridge, Mass., residence — a room now displayed as a national treasure at the Smithsonian Institution.

But the sides part on whether Thermador required the approval of the Julia Child Foundation for Gastronomy and the Culinary Arts, the Santa Barbara, Calif., charitable foundation to which she left her intellectual property, including trademarks, copyrights and the use of her likeness.

There seems no chance that Thermador would have received permission if it had sought it.

“The foundation feels really strongly about continuing to conduct itself as Julia would have. And she was adamant that she not personally endorse products or brands,” said Todd Schulkin, the foundation’s intellectual property manager.

When Child rose to prominence in the 1960s, there were other television chefs, including James Beard and Dione Lucas, who endorsed many products on their programs. Prud’homme, her great nephew, said Child was wary of anything that would undermine her life’s work as a “teacher of cookery.”

“She saw other chefs . the products they endorsed weren’t always of the highest quality, and she saw that could devalue their cultural currency, and she didn’t want to fall into that trap, said Prud’homme, who co-authored the memoir “My Life in France” with Child.

She was unwavering in her refusal to be a pitchwoman, even suing a restaurant that had boasted publicly that it was her favorite. In the early 2000s, she stopped by a restaurant in Los Angeles’ Chinatown neighborhood for dim sum and was asked to pose for photos with the staff. Child agreed only after every employee had agreed the pictures would never be used for commercial purposes.

The foundation discovered that Thermador was using her photos and name this summer. Child’s pop culture cachet has increased since her 2008 death, with new books about her life and the 2009 film “Julie & Julia” and the foundation has stepped up vigilance for copyright infringement.

“It took us some amount of time for us to see the extent to which (Thermador and its ad agency) were using that connection, and it seemed to develop in magnitude over time,” said Schulkin, who was a friend of Child.

After demanding that Thermador cease in July, the foundation was approached by DGWB, a Santa Ana, Calif., ad agency running the campaign, about securing the rights. The foundation’s lawyers refused and told Thermador it planned to file suit, according to correspondence provided by the foundation.

Thermador removed the materials from its website, but its parent company, BSH Home Appliances, filed a suit in Boston on Friday asking a federal judge to make a legal declaration that it had the right to use Child’s connection to the brand in its marketing materials. In its complaint, BSH’s lawyers wrote that the company’s use of Child’s photo and name “do not state or imply any endorsement” but “reflect on the long history, significance and influence of Thermador products on American society and culture.”

Thermador and DGWB declined comment.

Child’s foundation filed its own suits Monday in federal court in Los Angeles and state court in Santa Barbara, accusing Thermador and their ad agency of misappropriating intellectual property. The suits demand millions of dollars in damages as well as a cut of any profits derived from the invocation of Child’s name to be paid to the foundation, a nonprofit that supports culinary causes.

Thermador’s material makes “it appear as though Julia Child has been a company spokesman,” the federal suit stated. Child, the foundation’s lawyers wrote, “could have created a lifestyle brand like Martha Stewart or Oprah Winfrey, and endorsed major corporations and product manufacturerers, like Thermador and others, for large sums of money.”